1. Technical Field
The present invention relates generally to transmitting data over asynchronous transfer mode (ATM) networks according to the Internet Protocol (IP). More specifically, the present invention relates to providing redundant address resolution protocol (ARP) servers and default gateways which enhance the reliability of IP networks implemented using ATM technology.
2. Description of the Related Art
Due to the widespread acceptance of the current IP standard for communicating data, this standard has been adapted for use with ATM devices. Currently, the standard solution for natively sending IP traffic over an ATM interface is specified by the Internet Engineering Task Force (IETF) and is described by M. Laubach in a document entitled "Classical IP and ARP over ATM," RFC 1577, Hewlett-Packard Laboratories, January 1994.
Using the particular benefits of ATM technology, clients connected to an ATM network which supports IP can be grouped together into logical IP subnets (LISs). Membership in a particular LIS is not based on the physical location of the station. Instead, logically related stations are grouped together into the same LIS. Adding and removing stations from a LIS is very simple, due to the ease with which a client can register with an ARP server.
In addition to clients, other components are usually associated with a LIS. An ATMARP server is usually connected to a LIS. The role of an ATMARP server is to provide IP-to-ATM address mappings to requesting ATMARP clients. Also, a LIS is usually connected to a default gateway. A default gateway provides routing services for hosts that do not run routing topology protocols (e.g., open shortest path first (OSPF)--a link-state routing protocol specified by the IETF). Such hosts are commonly configured with the IP address of their default gateway.
In previous ATM systems, both the ATMARP server and the default gateway were potentially single points of failure. If the ATMARP server failed, ATMARP clients would no longer be able to resolve IP addresses to ATM addresses, and would therefore not be able to establish new virtual channel connections (VCCs). Also, the failure of the ATMARP server would result in ATMARP clients not being able to refresh existing mappings via the ATMARP server. Thus, the failure of an ATMARP server would severely reduce the communication capabilities of the LIS to which it was attached. The failure of a LIS's default gateway results in the hosts which are configured with the IP address of the failed default gateway losing routing services. The loss of routing services results in these hosts not being able to communicate with stations on other subnets.
Providing backup ATMARP servers and default gateways would eliminate the single points of failure. Such backup devices should be able to quickly and efficiently take over the responsibilities of the primary device if the primary device fails. Also, it would be desirable for the backup ATMARP servers and default gateways to integrate easily into existing systems, and to employ simple and reliable methods for taking over the responsibilities of the failed primary device, and of relinquishing control when the primary device comes back on-line.